The present invention relates to devices for wetting dry particles with a liquid. More specifically the invention relates to an apparatus which is particularly suitable for wetting dry powdered or granulated polymer with water to obtain lump free solutions of polymer.
For industrial purposes, it is frequently necessary to rapidly combine streams of liquids and solids to form solutions on a continuous basis. For example, homogenous solutions containing viscosity enhancing polymers must be supplied at a high rate to oil well drilling rigs where they are employed to facilitate the drilling process. The problems of and requirements for continuously forming uniform solutions by mixing powdered or granulated solids with liquids have thus been researched extensively. But, no suitable means for wetting hard-to-wet materials, such as certain polymers, has heretofore been discovered.
It has been particularly difficult to devise a wetting apparatus sufficiently compact to be used at a remote and/or crowded site such as an off-shore drilling platform.
Furthermore, it has not been possible to continuously form high-quality solutions of hard-to-wet dry materials without releasing substantial amounts of dust into the atmosphere as an airborne pollutant. The escape of dust is particularly undesirable because airborne dust forms a film on walking surfaces around the wetting device. Such dust, e.g. polymer dust, is extremely slippery when wet and thus is a safety hazard to workers.
As in all installations where finely divided material is handled, the escape of airborne particulate material should be minimized to avoid potential combustion.
Also, if a wetting apparatus is to be used in the presence of combustible gases, it must be free of ignition sources.
One of the difficulties of forming solutions from hard-to-wet powders or granules is that the powder tends to form small lumps. In most traditional mixing devices, such lumps become wetted before they break up into individual particles. The wetted surface of a lump becomes an impermeable film which hinders break up of the lump. Thus, lumps are carried through the mixer with powder inside remaining substantially dry and unmixed with liquid. Such lumping problems are especially troublesome when the powder comprises dry polymers. It is, however, a problem in wetting carbon dust and a number of other types of materials.
Another problem of typical wetting systems is that fine particles of dust from the powder become airborne and drift onto interior surfaces of the wetting apparatus. When such surfaces are moist but not washed, a wet paste builds up to plug passages of the apparatus or to form large, indivisible lumps which fall into the solutions.
A variety of devices have included features to deal with one or more of the above problems. But, heretofore, no apparatus has been devised which can successfully mix hard-to-wet powders, such as polymers, or successfully manage the dusting problems which result when such powders are dissolved on a continuous basis.
U.S. Pat. No. 1,980,499 to Pfaff, shows a dust quencher for water gas apparatus. Such a device could not be successfully used to form a solution containing hard-to-wet powders due to an inadequate array of nozzles and the presence of numerous unwashed surfaces which would encourage powder buildup.
Similarly, the spray apparatus described by C. P. Lamb et al, in U.S. Pat. No. 2,071,846, could not adequately wet hard-to-wet powders or prevent internal buildups of dust lumps.
U.S. Pat. No. 2,528,514 to Harvey et al shows a conical mixing vessel into which phosphoric acid is injected through peripheral inlets. Although the lower conical surfaces of this apparatus would be washed, a substantial dusting problem would remain. Furthermore, the simple vortical mixing illustrated would create a substantial lumping problem if used to wet a hard-to-wet powder such as polymer.
A wide variety of other devices have been constructed to facilitate the contact of liquids and solids. But none is adequate for mixing hard-to-wet powders such as polymers.